Rutherford
Rutherford was working with radioactive uranium. He applied a very strong magnet to the rays
given off by the uranium and discovered it was actually 3 rays: gamma, beta and
alpha. The alpha rays were made of
massive, + charged particles. He decided
to use these as “bullets” to explore the inner structure of the atom.
He fired them at a
thin gold foil. Because they had so much
mass, he expected they would go straight through. Most did go straight through, but some were deflected
and scattered in odd directions. Some
even bounced straight back!
The alpha particles must have hit something. For an alpha particle to bounce back, the
mass of an atom must be concentrated in a tiny area carrying a + charge. Rutherford had discovered the nucleus. The - charged electrons must be moving to
avoid getting pulled into the + charged nucleus. This is just like our planets moving around
the sun to avoid getting sucked in by its gravity. For this reason, Rutherford’s
model is called the planetary model.
Rutherford later found there were positively charged
particles within the nucleus so he also discovered protons.
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